Cushioning device for hydraulic cylinders

ABSTRACT

A cushioning device for the reciprocable piston of a hydraulic cylinder having a valve associated with the piston to be automatically shiftable by fluid flow and pressure fluctuations to progressively restrict flow from the cylinder as the piston reaches the end of its retraction stroke, but to allow substantially unrestricted fluid flow into the cylinder to move the piston in the opposite direction.

United States Patent [193 Bridwell et al.

[ Apr. 9, 1974 CUSHIONING DEVICE FOR HYDRAULIC CYLINDERS [75] Inventors:John W. Bridwell, Peoria; James C.

Goade, Joliet, both of Ill.

[73] Assignee: Caterpillar Tractor Co., Peoria, Ill.

22 Filed: Dec. 27, 1971 21 App]. No.: 212,129

[52] US. Cl. 91/409 [51] Int. Cl. FlSb 15/22 [58] Field of Search91/408, 409, 407, 405; 92/85 [56] 7 References Cited UNITED STATESPATENTS 3,296,942 1/1967 Nelson 92/85 1,844,107

2/1932 Sheperdson 91/409 4/1966 Aslon 91/408 3,247,767 3,314,657 4/1967PrudHomme et al 91/408 3,323,422

6/1967 'Freese 91/409 Primary ExaminerPaul E. Maslousky Attorney, Agent,or Firm-Fryer, Tjensvold, Phillips & Lempio 57 I ABSTRACT A cushioningdevice for the reciprocable piston of a hydraulic cylinder having avalve associated with the piston to be automatically shiftable by fluidflow and pressure fluctuations to progressively restrict flow from thecylinder as the piston reaches the end of its retraction stroke, but toallow substantially unrestricted fluid flow into the cylinder to movethe piston in the opposite direction.

4 Claims, 3 Drawing Figures PM'ENTEDAPR 9 i974 SHEU 1 8f 2 INVENTORSJOHN W. BRIDWELL JAMES C. GOADE m w w A iATENH-IH a law: 3302.319

sum 2 or 2 INVENTORS JOHN W BRIDWELL. JAMES C. GOADE ATTORNEYS 1CUSHIONING DEVICE FOR HYDRAULIC CYLINDERS."

BACKGROUND OF THE INVENTION It is frequently desirable to provide acushioning mechanism in a hydraulic cylinder for decelerating pis-- tonmovement in a controlled manner as the piston approaches the end of itsstroke. Many such cushioning devices are used commercially, but in mostcases they are unduly complex and costly to manufacture.

SUMMARY AND OBJECTS OF THE INVENTION Accordingly, it is an object of thepresent invention to provide an efficient, non-complex and inexpensivecushioning device for use in hydraulic cylinders.

Another object is to provide an improved cushioning device readilyadaptable to progressively restrict the flow of fluid out of a hydrauliccylinder during its retraction stroke, particularly as the piston nearsthe end of such stroke, and yet provide substantially unrestricted fluidflow into the cylinder during its extension stroke.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a cross sectional view of aportion of a hydraulic cylinder utilizing the cushioning device of thepresent invention therein; 7

FIG. 2 is a sectional view of the cylinder taken along line lI-Il inFIG. 1;and

FIG. 3 is a cross sectional view similar to FIG. 1, but illustrating analternative embodiment of the cushioning device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, acushioning means is attached to a piston 12 of a hydraulic cylinder 13.The piston is reciprocally mounted in a bore 14 of a tubular housing 16of the cylinder. The housing has an inletoutlet port means 18 formedthrough a sidewall thereof which communicates with a conduit 20, adaptedto selectively communicate with a source of pressurized hydraulic fluidor a sump via conventional control means (not shown). The port means islocated closely adjacent to a closed end 22 of the cylinder.

The piston is secured to a rod 24 by a lock nut 26 and is provided witha reduced diameter section 28 to further provide a shoulder of thepiston. The section is provided with an annular groove 30 which seats asnap ring 32 therein. An expansible chamber 34 is defined between thepiston, the closed end of the cylinder and the housing to communicatewith port means 18 and conduit 20.

Cushioning means 10 comprises a valve member constructed in the form ofa cup-shaped annular member comprising a ring 36 and a radially inwardlyextending flange 38. A central opening 40 of the flange has asubstantially larger diameter than the outer diameter of section 28 ofthe piston. Flange 38 is retained axially by retention means comprisinga shoulder of piston 12 and an annular washer 42 which abuts snap ring32. Ring 36 has a plurality of annular grooves 44 formed on its outerperiphery. As best shown in FIG. 2, the ring has an outer diametersubstantially smaller than the inner diameter of bore 14.-

OPERATION FIG. 1 illustrates piston 12 at the end of its retractionstroke wherein the piston has moved leftwardly to exhaust fluid fromchamber 34, through port 18 and into conduit 20. When ring 36 starts tocover the port, a pressure drop occurs across the port to force the ringupwardly. As shown in FIG. 2, substantial surface portions of the ring,along an arcuate segment thereof, move into substantial abutment withsidewall portions of the housing adjacent to the port.

In this manner, fluid flow out of the port is progressively restrictedas the ring covers the port to decelerate the piston as it approachesthe end of its retraction stroke. In order to prevent complete blockageof the port, annular grooves 44 are machined externally on the ring toprovide an orifice affording limited continuous communication betweenchamber 34 and conduit 20.

During the extension stroke of cylinder operation, pressurized fluidfrom conduit 20 forces ring 36 radi- 'ally inwardly to provideunrestricted fluid flow from port 18 to chamber 34.

FIG. 3 is a cross sectional view similar to FIG. I, but illustrating amodified cushioning device. Like numerals' are used to depictcorresponding constructions with such numerals appearing in FIG. 3 beingaccompanied by an a. i

A cushioning means 10a is attached to a piston 12a of a hydrauliccylinder 13a. The piston is reciprocally mounted in a bore 14a definedin a tubular housing 16a having an inlet-outlet port means 18a formedthrough a sidewall thereof to communicate with a conduit 20a. Althoughthe cushioning means is employed at the rod end of the cylinder, itcould readily be adapted for use at the head end thereof, as suggestedby FIG. I.

The piston is secured to a rod 24a by lock nut 26a. An annular washer 27is press-fitted (e.g., 0.0005-0.000l5 in. press-fit) or otherwisesuitably secured on rod 24a to abut piston 12a. The washer comprises anannular recess forming a eircurnferentially extending reduced diametersection or ledge portion 28a and a radially extending flange 29.Cushioning means comprises a cup-shaped valve means or member comprisinga ring 36a, having smooth and uninterrupted radially outer surfaceportions, and a radially inwardly extending flange 380.

A central opening 40a of the flange has a larger diameter than the outerdiameter of ledge portion 28a of washer 27. The flange is retainedaxially by retention means comprising an annular slot defined betweenradial portion 29 of the washer and piston 28a. In addition, ring 36ahas a diameter which is less than the inside diameter of bore 14a topermit limited radial movements of the valve member.

OPERATION FIG. 3 illustrates piston 12a at the end of its extensionstroke to exhaust fluid from the rod end of the cylinder. When ring 36abegins to cover port 18a at its leading, frusto-conically shaped freeend-31 remote from flange 38a, fluid forces generated by fluid flow andthe resulting pressure drop occasioned across the ring function to moveouter surface portions of the ring into masking relationship with port18a. Fluid flow out of conduit 20a is thus progressively restricted todampen the retraction stroke.

Such restriction creates a pressure build-up in the head end of thecylinder whereupon a suitably calibrated pump relief valve (not shown)will open to reduce the flow to such head end and the linear speed ofthe piston will be reduced. Since the outer diameter of ring 360 isslightly smaller than the inner diameter of bore 14a, port 18a will notbecome fully blocked in its FIG. 3 position, During retraction of piston120, leftwardly in FIG. 3, pressurized fluid from conduit 20 will forcering 36a radially upwardly away from inlet port 18a to providesubstantially unrestricted fluid flow into expansible chamber 34a.

What is claimed is:

l. A hydraulic cylinder comprising a tubular housing, a pistonreciprocally mounted on a rod in said housing to define an expansiblechamber therewith, port means formed through a sidewall of said housing,adjacent to a closed end thereof, for communicating a pressurized fluidto said chamber and cushioning means solely responsive to fluid flowbetween said chamber and said port means for gradually restricting fluidflow from said chamber to said port means when said piston moves axiallytoward said port means and for permitting substantially unrestrictedfluid flow from said port means to said chamber when said piston movesaxially away from said port means, said cushioning means comprising anannular member of cup shape having a ring with an outside diameter whichis substantially smaller than the inside diameter of said housingpositioned to move radially outwardly into abutment with said sidewallsolely in response to exhaust fluid flow to at least substantially coversaid port means and an integral, radially inwardly extending flange andannular retention means comprising a washer secured to said rod abuttingsaid piston and defining a shoulder of reduced diameter and a radialportion of greater diameter to define an annular slot capturing saidflange between said radial portion and said piston for guiding radialmovement of said ring relative to said port means.

2. The invention of claim 1 wherein radially outer surface portions ofsaid ring are smooth and uninterrupted and terminate at afrusto-conically shaped free end of said ring, remote from said flange.

3. A cushioning device in combination with a piston disposed on a rod ina hydraulic cylinder having a fluid inlet-outlet port formed through ahousing thereof, said cushioning device comprising valve means looselydisposed within said housing and being positionable by the piston intoradial alignment with said port during retraction of the piston andbeing shiftable radially outwardly solely by fluid discharged from thecylinder to move into masked relationship over said port, said valvemeans comprising an annular ring member with an outside diameter whichis substantially smaller than the inside diameter of said housingpositioned to move radially outwardly into abutment with said housing toat least substantially cover said port and having a radially inwardlyextending flange secured thereto, and retention means comprising awasher secured to said rod abutting said piston and defining a shoulderof reduced diameter and a radial portion of greater diameter to definean annular slot capturing said flange between said radial portion andsaid piston for guiding radial movement of said ring relative to saidport.

4. The invention of claim 3 wherein said valve means cooperates withsaid housing to form flow restricting means gradually providing arestricted passage for fluid discharged to said port to deceleratepiston movement by causing a pressure drop across said port to maintainthe ring of said valve means in said masked relationship and beingmovable radially inwardly out of said masking relationship in responseto fluid flow from said port to said cylinder to permit substantiallyunrestricted fluid flow thereby.

1. A hydraulic cylinder comprising a tubular housing, a pistonreciprocally mounted on a rod in said housing to define an expansiblechamber therewith, port means formed through a sidewall of said housing,adjacent to a closed end thereof, for communicating a pressurized fluidto said chamber and cushioning means solely responsive to fluid flowbetween said chamber and said port means for gradually restricting fluidflow from said chamber to said port means when said piston moves axiallytoward said port means and for permitting substantially unrestrictedfluid flow from said port means to said chamber when said piston movesaxially away from said port means, said cushioning means comprising anannular member of cup shape having a ring with an outside diameter whichis substantially smaller than the inside diameter of said housingpositioned to move radially outwardly into abutment with said sidewallsolely in response to exhaust fluid flow to at least substantially coversaid port means and an integral, radially inwardly extending flange andannular retention means comprising a washer secured to said rod abuttingsaid piston and defining a shoulder of reduced diameter and a radialportion of greater diameter to define an annular slot capturing saidflange between said radial portion and said piston for guiding radialmovement of said ring relative to said port means.
 2. The invention ofclaim 1 wherein radially outer surface portions of said ring are smoothand uninterrupted and terminate at a frusto-conically shaped free end ofsaid ring, remote from said flange.
 3. A cushioning device incombination with a piston disposed on a rod in a hydraulic cylinderhaving a fluid inlet-outlet port formed through a housing thereof, saidcushioning device comprising valve means loosely disposed within saidhousing and being positionable by the piston into radial alignment withsaid port during retraction of the piston and being shiftable radiallyoutwardly solely by fluid discharged from the cylinder to move intomasked relationship over said port, said valve means comprising anannular ring member with an outside diameter which is substantiallysmaller than the inside diameter of said housing positioned to moveradially outwardly into abutment with said housing to at leastsubstantially cover said port and having a radially inwardly extendingflange secured thereto, and retention means comprising a washer securedto said rod abutting said piston and defining a shoulder of reduceddiameter and a radial portion of greater diameter to define an annularslot capturing said flange between said radial portion and said pistonfor guiding radial movement of said ring relative to said port.
 4. Theinvention of claim 3 wherein said valve means cooperates with saidhousing to form flow restricting means gradually providing a restrictedpassage for fluid discharged to said port to decelerate piston movementby causing a pressure drop across said port to maintain the ring of saidvalve means in said masked relationship and being movable radiallyinwardly out of said masking relationship in response to fluid flow fromsaid port to said cylinder to permit substantially unrestricted fluidflow thereby.